The purpose of the proposed research is to investigate the effects of protein-calorie malnutrition (PCM) on the respiratory host defense system. A standard model of PCM in rats will be studied. Intrapulmonary clearance of aerosolized bacteria will be measured to assess respiratory host defense in vivo. In addition, alveolar macrophage function will be tested in vitro using assays of chemotaxis phagocytosis and microbicidal activity. The effects of PCM on respiratory host defenses in weanling animals and mature animals will be compared. The effects of PCM will also be compared with the effects of acute starvation, and the reversibility of abnormalities induced by PCM will be investigated by refeeding studies. These studies are intended to define the effects of PCM on the ability of the lung to inactivate inhaled organisms, and to clarify the cellular basis for these effects.